What is fragmentation? Different types of fragmentation?

Fragmentation occurs in a dynamic memory allocation system when many of the free blocks are too small to satisfy any request.

External Fragmentation: External Fragmentation happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. If too much external fragmentation occurs, the amount of usable memory is drastically reduced.

Total memory space exists to satisfy a request, but it is not contiguous

Internal Fragmentation: Internal fragmentation is the space wasted inside of allocated memory blocks because of restriction on the allowed sizes of allocated blocks.

Allocated memory may be slightly larger than requested memory; this size difference is memory internal to a partition, but not being used

Reduce external fragmentation by compaction

o   Shuffle memory contents to place all free memory together in one large block.

o   Compaction is possible only if relocation is dynamic, and is done at execution time.